A gas turbine includes a compressor that compresses atmospheric aft to generate compressed air, a combustor that combusts fuel in the compressed aft to generate combustion gas, and a turbine that is driven by the combustion gas. The compressor includes a compressor rotor that rotates about an axis and a compressor casing that covers the compressor rotor while allowing the compressor rotor to rotate. The turbine includes a turbine rotor that rotates about an axis and a turbine casing that covers the turbine rotor while allowing the turbine rotor to rotate.
A predetermined clearance (hereinafter, this clearance will be referred to as a tip clearance) is required between the outer end, in the radial direction, of a blade of the turbine rotor and the inner peripheral surface of the turbine casing. In terms of the turbine efficiency, it is desirable to minimize the tip clearance as much as possible.
Incidentally, after the gas turbine is stopped, the temperature of the turbine rotor disposed inside the turbine casing drops more slowly than that of the turbine easing, which is exposed to the outside air. Therefore, after the gas turbine is stopped, an amount of decrease in thermal expansion, per unit time, of the turbine rotor is less than an amount of decrease in thermal expansion, per unit time, of the turbine casing. Thus, after the gas turbine is stopped, the tip clearance is temporarily decreased. When the gas turbine is started in this state, the position of the outer end, in the radial direction, of the blade is displaced toward the outer side in the radial direction due to a centrifugal force acting on the turbine rotor, which in turn may cause the blade of the turbine rotor to come into contact with the inner peripheral surface of the turbine casing.
Hence, in the technology disclosed in Japanese Unexamined Patent Application Publication No. H11-050809A, at the startup of the gas turbine, the turbine rotor is cooled by pressurizing air extracted from a gas turbine casing using a blower and supplying the air into the turbine rotor. In the technology disclosed in Japanese Unexamined Patent Application Publication No. H11-050809A, cooling the turbine rotor in the above-described manner to increase the tip clearance at the startup of the gas turbine prevents the blade of the turbine rotor from coming into contact with the inner peripheral surface of the turbine casing.